Production of vinyl chloride



Reissued June 21, 1949 PRODUGTIOlfl OF VINYL CHLORIDE Joseph F. Weiler, Lewiston, N. Y., assignor to M thi- No, Drawing.

Original N0.

son Chemicalporporatipma corpbrationl;

2,4l2,308, dated;

'Decen ber.10,1946,l Serial No. 538,088, May 1944;, Application, for reissueApi-ilfl,

see! He.- 8 4.

1-Claim. (Cl. 260656 This invention relates to improvements in the productionofvinyl chloride fron ethyleneidi-f over. an activate'd adsorbent, and, to the remaim ingvunadsorbed decomposition products, is added acetylene, and, in some'instances, hydrogen ch lo-" ride, and the hydrogen chloride and acetylene are catalyticallyv combined'toform vinyl chloride.

The catalyticcombination of hydrogen chloride and acetylene to form vinylchloride is known, Catalysts which may be'used in clude mercuricchlorideand mixtures of mercuric chloride and alkali or. alkaline earth chlorides, which may be deposited on the carrier'such as silica gel, or activatedcarbon. Ordinarily temperatures 0151186 to 250 OL-are used. The reactionis strong 1y.- exothermic, and control of the temperature difficult to obtain.

The process of the present invention affords a. substantial improvement over previously suggested'processes forthe production of vinyl chloride in that when to the decomposition products of -.ethylene dichloride, surviving;v contact with the activated adsorbent, isv added the necessary amount of :acetyleneto combine with. the. hy-' drogen chloride, there is formed a mixture of vinyl-chloride, acetylene and hydrogen. chloride. Whensu-cha gas mixtureis passed .over an appropriate. catalyst; for theaddition of. the hydrogen chloride to theacetylene, under the usual temperatureand pressure conditions, the vinyLchloride servesas, adiluent which prevents any unduerisein thetemperatureof the catalyst, and overcomes anumber .of 1 the diifficulties heretoi ore encounteredin ,controllingthe temperature of the. ata yst- It -hasheretoforebeen proposed to prevent undue rise in temperature of the catalyst in thecat, alytic combination of acetylene and hydrogen chlorideby .the use; oi-suchdnert diluentsas hydrogen, carbon monoxide, and the like, but the use of. such. diluents introduces a number of op- I "ties, which. are not encountered: when vinyl fchlor detispresent;to prevent the catalyst frorhoverheating, Thus the vinyl chloride is recovered from. the reaction product by cooling. and condensing." Whenvinyl chloride is used as thedilunt, its p artialpressureis such that a good wave-yrs nose. Fixe a s. ch as. hy. drh'gen, carbon, oxide and theJike. interfere wi h; he ps ier-y llQYiQYLQhIO iQQ bec use.

of the low partial pressure" of vinyl chloride in the reactionproduct,"- to "an extent which makes economical'recovery difficult or impossible. Fur-' thermore, vinyl chloridehas 'a considerably high- I erheat capacity 'thanihe' gases heretofore suggested as diluents in thetemperatur'e range used in th catalytic combination, namely, by th 250 C., and therefore is amore'efiic'ient tempering medium. It produces no undesirable byproducts as 'may belproduced with hydrogen, hydrogen sulfide,'carbon monoxide and other previously suggested gases, including excess acetylene, which tends to polymerize.

The pyrolysis of the ethylene dichloride, the

.Ifirststep in the process,v ordinarily results'in the formation of some. acetylene, as well as vinyl chloride and hydrogen chloride, but. any acetylene stantially interferewith the efii-ciency of the process.

The pyrolysis of the ethylene dichloride is carried out in the usual way, advantageously "without the use of a catalyst, byv passing the ethylene dichloride through pyrolysis equipmentat a temperature of 575-600 C. The mixture. of products of pyrolysis is thenpassed through a bed of activated. carbon or similar. adsorption agent before bringing it intolcontact with the catalyst,

as, by such procedure, the life ,of the catalystis lengthened,- presumably through the removal of sornematerial, the, nature of which at present isnot known, which poisonsor inactivates the,

catalyst.

The acetylene which. is, used in the reaction may be obtained from any convenient source, and

may be a relatively pure productv or may contain, considerable proportions of diluent, such as other. hydrocarbons, which are non-reactive in the.

culties, incident to the, generation oi heat by the,

exothermic reaction, and the less the difiiculties vinyl chloride inapurestate.

In practicing the present invention, ethylene dichloride is passed through suitable pyrolysis equipment, where it is heated to around 575-600" C. with conversion of most of the ethylene dichloride to vinyl chloride and hydrogen chloride, with some formation of acetylene. The resulting gas mixture is then passed through a bed of activated carbon or similar adsorption agent. Acetylene is added to the resulting gas mixture, which is then passed through a catalyst bed composed of a suitable catalyst and maintained at a temperature of 180-270" C. Hydrogen chloride and acetylene should be present in the gaseous reaction mixture in approximately stoichiometric proportions. Thus, acetylene may be added to the adsorbent treated products of pyrolysis in the proportions required to react with the hydrogen chloride there present in excess of the proportion of acetylene there present, or both hydrogen chloride and acetylene may be added to the adsorbent treated products of pyrolysis, with the total acetylene and hydrogen chloride in the final mixture adjusted to approximate molar equality. The amount of vinyl chloride in the gas mixture will ordinarily be about one-third of the total feed (gas volume basis), which is the proportion obtained if only acetylene be added to the products of pyrolysis; but by the addition of extraneous vinyl chloride, or hydrogen chloride and acetylene, other proportions of vinyl chloride may be present in the gas mixture, and the amount of vinyl chloride will usually be between 15% and 50% (gas volume basis) and may be as high as about 75%.

The vinyl chloride in the exit gases is recovered by cooling and condensing the gases, and fractionally distilling the condensate. Yields of vinyl chloride ranging up to 90%, based on the ethylene dichloride used, are readily obtained, while yields ranging up to 99% based on the acetylene are obtained. The catalyst is easily kept at reaction temperature, without any special means for cooling, and remains active for long periods, in contrast with the behavior of such catalysts in operations in which the catalyst temperature rises, frequently to 400 C., in which the catalyst rapidly deteriorates.

The invention will be illustrated by the following examples, but it is not limited thereto.

Ewample 1.Ethylene dichloride (1,2-dichloroethane) was vaporized at the rate of 0.5 mole /hr. through a Pyrex glass pyrolysis tube of 225 ml. volume maintained at 575-600 C. The exit gases (pyrolysis products) were then conducted through a water-cooled condenser into a mixing chamber where acetylene was introduced at the rate of 0.5 mole/hr. The absence of condensate in the condenser indicated substantially complete conversion of the ethylene dichloride. The mixture was then passed over a catalyst consisting of a mixture of mercuric chloride and potassium chloride deposited on activated charcoal. A glass catalyst tube provided a catalyst bed 5.5 cm. in cross-section and 40 cm. in length. Two separate resistance wire windings on the catalyst tube provided means for externally heating the initial and final 20 cms. of the catalyst bed independently of each other. A thermocouple tube running through the longitudinal axis of the catalyst bed permitted exploration of the temperature at various points in the bed. Before passage of the mixture of acetylene and pyrolysis products through the catalyst bed, the initial 20 cm. of said catalyst bed was raised to 240-250 C. and the final 20 cm. to 180-190" C. by means of the resistance wire FY H) heaters. As soon as the passage of the mixture of acetylene and pyrolysis products through the catalyst bed was started, the external heating of the initial 20 cm. of catalyst bed was discontinued. Heat of reaction was almost immediately discernible by an increase in temperature of the first 4-5 cm. of the catalyst bed. The temperature at this point in the catalyst bed rose to a maximum of 270 in a few minutes while deeper in the catalyst bed the temperature fell progressively. With continued passage of the gas the 4-5 cm. hot spot progressed deeper into the catalyst bed (maintaining a maximum temperature of 270 at the hot spot) while the forward end of the catalyst bed began to cool indicating a loss in activity of the catalyst at this point. The hot spot had transversed the initial 20 cms. of the catalyst bed after 5 hrs. of operation at which time the process was stopped.

The final product was caught in a trap cooled with a solid COz-acetone mixture and then fractionally distilled. There was recovered 4.5 moles of pure vinyl chloride which is per cent of the theoretical yield.

Example 2.Pyrolysis of ethylene dichloride was carried out as described in Example 1. The

pyrolysis products after leaving the water-cooled condenser were passed through a trap containing 455 ml. of activated charcoal at room temperature before being mixed with the acetylene. The mixture of acetylene and pyrolysis products thus obtained were passed over the same catalyst preparation under the same conditions as described in Example 1. The hot spot temperature was 270 C. The hot spot at the end of 4 hours of operation had progressed only an inch into the catalyst bed, thus demonstrating the beneficial act-ion of the activated charcoal treatment of the pyrolysis products in prolonging the life of the catalyst. By fractional distillation there was received 3.8 mols of pure vinyl chloride or 84.4 percent of the theoretical yield.

Example 3.Ethylene dichloride was pyrolyzed,

and the products mixed with acetylene as in Example 1. The mixture was passed over a small surface of mercury heated to 300 C. and thence through a catalyst bed consisting of activated charcoal which was heated externally sufficiently to maintain a temperature of 250 0. when no gas was passing through it. Passage of the reaction mixture through the catalyst bed without reducing the supply of external heat resulted in an in- I crease in temperature to 265 C. throughout the catalyst bed with no pronounced hot spot. The reaction mixture after passing through the activated charcoal was passed through an additional reactor containing a catalyst consisting of mercuric chloride and potassium chloride deposited on activated charcoal and maintained at 180 0. Only a slight increase in temperature occurred in this catalyst bed. Pure Vinyl chloride to the extent of 87.7% of the theoretical yield was obtained.

Example 4.Ethylene dichloride was pyrolyzed over an activated alumina catalyst at 450 C. at the rate of 0.5 mole/hr. The resulting pyrolysis products were passed through a trap containing activated charcoal at room temperature, then mixed with acetylene (0.5 mole/hr.) and-the mixture treated exactly as in Example 2. The maximum temperature of the hot spot was 270 C. and the hot spot had not progressed discernibly into the catalyst bed after 6 hours of operation. Pure vinyl chloride to the extent of 68.5% of the theoretical yield was recovered. The low yield'is 6 of pyrolysis over an activated adsorbent, adding acetylene to the adsorbent treated products of pyrolysis, and catalytically reacting the acetylene with the hydrogen chloride in the mixture.

JOSEPH F. WEILER.

No references cited. 

